This invention relates to a heat transfer image-receiving sheet useful in a heat transfer method by use of a sublimable dye (heat migratable dye). More particularly, the invention is intended to provide a heat transfer image-receiving sheet which can perform high speed recording and also form a transferred image of high density and high resolution without use of a conventional release agent, and yet has excellent oil resistance of the image formed such as fingerprint resistance and plasticizer resistance, etc.
As the method for giving excellent mono-color or full-color images simply and at high speed in place of the general letter printing method or printing method of the prior art, the ink jet system, the heat transfer system, etc. have been developed. Among them, as the system which can give full-color images having excellent continuous gradation comparable with color photography, the so called sublimation heat transfer system by use of a sublimable dye is the most excellent.
The heat dye transfer sheet used in the above-mentioned sublimation type heat transfer system generally employed is one having a dye layer containing a sublimable dye formed on one surface of a substrate sheet such as polyester film, etc., while on the other hand, having a heat resistant layer provided on the other surface of the substrate sheet for prevention of sticking of the thermal head.
By superposing the dye layer surface of a such heat dye transfer sheet on the heat transfer image-receiving sheet having an image-receiving layer comprising a polyester resin, etc., and heating imagewise from the back surface of the heat dye transfer sheet with a thermal head, the dye in the dye layer is migrated to the heat transfer image-receiving sheet to form a desired image.
In the heat transfer system as described above, there is an excellent advantage that the density of the image can be exhibited depending on the temperature of the thermal head. However, when the temperature of the thermal head is increased for making the density higher, the binder forming the dye layer is softened and stick to the image-receiving sheet, thus causing an inconvenience that the heat transfer sheet and the image-receiving sheet are adhered. In an extreme case such adherence results in a problem that the dye layer is peeled off during peeling of the heat transfer and image-receiving sheets to be transferred onto the image-receiving sheet surface.
As the method for solving such problem, it has been practiced to incorporate a release agent such as silicone oil, etc. in the dye receiving layer of the image-receiving sheet. However, since said silicone oil is liquid at room temperature, it has the drawback that it bleeds out onto the surface of the receiving layer during storage to cause such problem as blocking or contamination. On the other hand, there are also methods in which a thermosetting silicone oil is used, but in these methods, heating is required after formation of the receiving layer, whereby there is the problem that the production steps are very cumbersome.
Further, if a relatively large amount of silicone is added for giving sufficient releasability to the receiving layer, there ensues such problems that dye receptivity is lowered or the image-receiving sheet is discolored to adversely affect storability.
Also, although the above-mentioned methods have excellent peelability, there is involved the problem that when the image obtained is touched with fingers, fingerprints are transferred, and the dye where the fingerprints are transferred is discolored. Also, when such image is brought into contact with a polyvinyl chloride resin containing a plasticizer or a plastic erasing rubber containing a plasticizer, the dye is migrated which causes the image to be similarly discolored.